Apparatus for removing interconnects to separate two parts of a workpiece

ABSTRACT

Disclosed is an apparatus for separating interconnects between, for example, a card and a substrate. The apparatus includes one or more rotationally biased (e.g., spring-loaded, etc.) partial-circle structures (e.g., blades, squeegee, plow, etc.) and one or more temperature-sensitive releases connected to the partial-circle structures. The partial-circle structures are positioned to rotate and separate the interconnects when released by the temperature-sensitive releases. The invention can also include solder reservoirs positioned to receive solder from the interconnects separated by the partial-circle structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/838,946 filed Aug. 15, 2007, which is a continuation of U.S.application Ser. No. 10/680,622 filed Oct. 7, 2003, the completedisclosure of which, in its entirety, is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an apparatus and method forseparating integrated circuit structures connected by interconnects suchas ball grid arrays and column grid arrays.

2. Description of the Related Art

Ball Grid Arrays (BGA) and Column Grid Arrays (CGA) are widely used toelectrically and mechanically connect substrates (typically ceramic)carrying semiconductor chips to a card. The BGA commonly consists of anarray of metal balls which are soldered to a substrate by means of asolder fillet material. The solder fillet material is typically of alower melting temperature (183 C for eutectic Pb/Sn) than the solderball (˜280 to 300 C) which it is joining to, enabling the solder ballnot to melt during joining. However, the solder ball and fillet materialmay be of the same composition, thus causing the entire interconnect toreach liquidous temperature during the reflow. During the manufacturingprocess, a substrate, either organic or ceramic, is attached to acarrier. Typically, this carrier is organic and may be comprised of FR4like material, or may have Surface Laminar Circuitry (SLC) on a coremade of other organic material. If the substrate requires rework, suchas because of a defective chip, the substrate must first be removed fromthe carrier.

One conventional method to remove a substrate from a card uses hot gas.In such a method, a gas, typically nitrogen, is heated to hightemperatures and impinged upon the substrate. The tooling for such anoperation is dedicated. Further, such an operation is typicallyperformed in batch mode. There are numerous problems with employing sucha method when removing a ceramic substrate from an organic carrier.First, hot gas uses a significantly greater amount of thermal energythat is transmitted to the top surface of the substrate. Such hightemperatures can damage the still good chips atop the substrate, or makefailure analysis for the defective chips not possible. The formersituation may arise when the substrate has two or more chips, with onebeing defective, and the others being good. More importantly, suchmethods cannot be used for higher liquidous temperature alloys, such asthose being developed for lead free applications, because the higheramount of heat input would damage organic boards which typically cannotexceed temperatures greater than 250 C. As an example, a lead-free alloycomprising Sn, Ag and Cu (95.5 wt % Sn, 3.8 wt % Ag and 0.7 wt % Cu) hasa liquidous temperature equal to approximately 217 C. The hot gastechnique can cause excessively high temperatures at the organic boardor carrier surface, when it attempts to melt this lead-free alloy whichresides between the ceramic substrate and organic board. Thus, a needexists to separate the substrate from the carrier while preserving itsability to be rejoined to another carrier.

SUMMARY OF THE INVENTION

The invention provides an apparatus for separating interconnectsbetween, for example, a card and a substrate. The apparatus includes oneor more rotationally biased (e.g., spring-loaded, etc.) partial-circlestructures (e.g., blades, squeegee, plow, etc.) and one or moretemperature-sensitive releases in contact with the partial-circlestructures. The partial-circle structures are positioned externally tothe interconnect area and rotate though the interconnect area andseparate the interconnects when released by the temperature-sensitivereleases. The invention can also include solder reservoirs positioned toreceive the removed solder from the interconnects that are separated bythe partial-circle structures.

The rotational paths of the partial-circle structures can partiallyoverlap. Each of the temperature-sensitive releases can be different,such that each of the partial-circle structures is released at adifferent temperature. Thus, the partial-circle structures will rotatesequentially (at different times) to prevent any potential contactbetween rotating partial-circle structures.

The workpiece (e.g., carrier and substrate having one or more integratedcircuit chips) is positioned between the partial-circle structures. Thepartial-circle structures rotate around axis external to the workpiece.The partial-circle structures pass between two parts of the workpiece(e.g., between the carrier and substrate and/or between the chip andsubstrate) when released by the temperature-sensitive releases. Thepartial-circle structures break interconnects between such parts of theworkpiece when released by the temperature-sensitive releases. Thetemperature-sensitive releases are adapted to release the partial-circlestructures at temperatures above a melting point of the interconnects.

Thus, the inventive apparatus separates devices joined withinterconnects. The invention provides partial-circle structures thatrotate and pass between the devices to be separated. The partial-circlestructures can be released sequentially and the interconnect materialthat is remove from the interconnect region by the partial circlestructure is collected in reservoirs to prevent contamination ofsurrounding devices and/or the tool. The invention simplifies andreduces the cost of separating devices by providing an apparatus inwhich the workpiece can be easily mounted and thereafter placed in anyconventional heating tool. The invention operates automatically and onits own to break the interconnects at the proper temperature. Further,the invention holds separated devices after removing theinterconnections to allow the devices to be easily inspected andreworked.

These, and other, aspects and objects of the present invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingpreferred embodiments of the present invention and numerous specificdetails thereof, is given by way of illustration and not of limitation.Many changes and modifications may be made within the scope of thepresent invention without departing from the spirit thereof, and theinvention includes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription with reference to the drawings, in which:

FIGS. 1A and 1B are schematic diagrams of interconnections between asubstrate and a carrier;

FIG. 2 is a perspective schematic drawing of the inventiveinterconnection removal device;

FIG. 3 is a top-view schematic drawing of the inventive interconnectionremoval device;

FIG. 4 is a side-view schematic drawing of the inventive interconnectionremoval device;

FIG. 5 is a side-view schematic drawing of the inventive interconnectionremoval device;

FIG. 6 is a schematic drawing of the paths through which the partialcircle structures rotate; and

FIG. 7 is a schematic drawing of the paths through which the partialcircle structures rotate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. It should be noted that thefeatures illustrated in the drawings are not necessarily drawn to scale.Descriptions of well-known components and processing techniques areomitted so as to not unnecessarily obscure the present invention. Theexamples used herein are intended merely to facilitate an understandingof ways in which the invention may be practiced and to further enablethose of skill in the art to practice the invention. Accordingly, theexamples should not be construed as limiting the scope of the invention.

The invention provides a method and apparatus that separatesinterconnections between a substrate and an underlying carrier. Althoughball grid array (BGA) interconnects are discussed below, the inventioncan equally be applied to other interconnect structures such as columngrid arrays (CGA), etc. The invention provides a low cost, highlyreliable method/apparatus that can easily be employed with existingtools (e.g., continuous belt furnace).

FIGS. 1A and 1B illustrate devices 14, 18 connected by solder balls 16in a ball grid array. For example, device 14 could be a substrateconnected to a carrier 18. Alternatively, device 14 could comprise anintegrated circuit chip mounted on a substrate 18. In both drawings,arrow 10 represents a separating force. The separating force 10 can beapplied to device 14 through separator/clamp 12 or can be applied to theinterconnects 16. The invention described below provides an apparatusthat moves structures through the interconnects 16 (as shown FIG. 1B) tobreak the interconnects 16. However, the invention can also apply theseparating force 10 shown in FIG. 1A to the device 14 to further assistin separating the devices 14, 18.

With the invention, the substrate and carrier are placed into a holdingfixture/apparatus 200 (FIGS. 2-5). The apparatus includes one or morerotationally biased (e.g., spring-loaded, etc.) partial-circlestructures 204 (e.g., half or quarter-wheel blades, squeegees, plows,etc.) and one or more temperature-sensitive releases 300, 302 (FIG. 3)in contact with connected to the partial-circle structures 204. Thepartial-circle structures 204 are positioned to rotate and separate theinterconnects 16 between the upper portion 14 (e.g., the substrate,chip, etc.) and the lower portion 18 (e.g., card (carrier), substrate,etc.) of the workpiece 202 when released by the temperature-sensitivereleases 300, 302. Item 200 represents the upper part of the frame ofthe apparatus and item 214 represents the lower part of the frame of theapparatus.

The invention can also include solder reservoirs 208 positioned toreceive solder from the interconnects separated by the partial-circlestructures. When the partial-circle structures 204 pass between theupper device 14 and the lower device 18, they push solder out frombetween the two devices 14, 18. The solder reservoirs 208 collect thesolder as it is pushed out from between the devices 14, 18. Thus, thesolder reservoirs 208 collect the solder that was previously used toform the interconnects to prevent the solder from contaminating thetools in which the apparatus will be used and/or adjacent devices.

The carrier 18 is locked into place, using product clamp 206, and a toparm (e.g., structure 12 or a similar structure) grips and locks thesubstrate 14 into a stationary position. At each corner of thecarrier/substrate 202, a quarter wheel 204 is spring loaded(rotationally biased). In one example, the thickness of each quarterwheel 204 can be approximately 0.010″, but could be more or lessdepending on the specific application. The partial-circle structures 204can be made of several possible materials, such as tungsten, hightemperature rubber, etc.

The workpiece 202 (e.g., carrier 18 and substrate 14 having one or moreintegrated circuit chips) is positioned between the partial-circlestructures 204. The partial-circle structures 204 rotate around axis(axel) 210 external to the workpiece 202. Preferably, the axis 210 arepositioned to be directly adjacent to each of the corners of theworkpiece 202. The partial-circle structures 204 pass between two partsof the workpiece 202 (e.g., between the carrier 18 and substrate 14and/or between the chip 14 and substrate 18) when released by thetemperature-sensitive releases 300.

The temperature-sensitive releases 300 are adapted to release thepartial-circle structures at temperatures close to or above the meltingpoint of the interconnects. Therefore, the interconnects 16 aresubstantially softened or liquefied before the releases 300 release thepartial-circle structures 204.

The temperature-sensitive releases 300 comprise actuation devices thatcan use bimetallic discs 302 to push a pin 300 out of an opening withina bracket 404. The bracket 404 is connected to the axis (axle) 210 aboutwhich the partial-circle structures 204 rotate through member 406. Inaddition, FIG. 5 illustrates a rotational shaft bushing 500 within whichthe shaft (axel) 210 rotates. The bracket 404 is rotationally biased bythe spring 402. When the pin 300 is released from the opening in thebracket 404, the axle 210 rotates by operation of the force of thespring 402 which causes the partial-circle structure 204 to rotate andpass between the upper device 14 and the lower device 18, therebyseparating the interconnects 16 between the devices 14, 18.

The rotational movement of the bracket 404 is limited by a stop member,such as the axel base 408 shown in FIG. 4. Therefore, in one embodiment,the partial-circle structures 204 will only pass between the upper 14and lower 18 devices a single time and will stop rotating after havingpassed between the devices (when the bracket 404 rotates into contactwith the axle base 408). As would be readily understood by oneordinarily skilled in the art, other similar structures can be used tocontrol the rotation of the bracket 404 and partial-circle structure204.

The torsion spring adjusters 212 allow the bracket 404 and thepartial-circle structures 204 to be returned to their rotationallybiased position. After being returned to the rotationally biasedposition, the pin 300 is inserted through the opening in the bracket 404to maintain the bracket 404 and partial-circle structure 204 in therotationally biased position.

At a prescribed temperature range, the bimetallic discs 302 actuate thequarter wheels 204. In other words, the bimetallic discs 302 expand whenheated and push the head of the pin 300 against bracket 400 which causesthe pin 300 to move out of the opening in the bracket 404. The apparatuscan be used with a continuous belt furnace which heats the interconnects16 and the bimetallic discs 302. Upon reaching liquefaction of theinterconnect metal or alloy 16, the quarter wheel 204 then sweepsthrough the gap between the substrate 14 and the carrier 18. In doingso, the quarter wheel 204 wipes the interconnects and removes theinterconnects from the package, and disposes the material into thereservoir 208. While bimetallic discs 302 are discussed above, as wouldbe recognized by one ordinarily skilled in the art, other devices suchas springs, etc. could be utilized instead of bimetallic discs as theforce trigger applied to the wheels.

Expansion of each bimetallic disc 302 is timed such that each quarterwheel 204 is actuated in series mode, one after another so as not tointerfere with each other. Thus, each of the temperature-sensitivereleases 302 can be different, such that each of the partial-circlestructures is released at a different temperature (and different pointin time). As the apparatus 200 is moved along the belt within a furnace,the temperature gradually increases. At each temperature increase, adifferent partial-circle structure 204 is released, as controlled byeach different temperature-sensitive release 302. Thus, thepartial-circle structures could rotate sequentially (at different times)to prevent any potential contact between rotating partial-circlestructures. After the last quarter wheel 204 sweeps through and removesthe last of the interconnects 16, the top arm 12 holds the substrate 14and prevents it from falling onto the carrier 18.

As shown in FIGS. 6 and 7, the rotational paths of the partial-circlestructures 204 may partially overlap. More specifically, FIG. 6illustrates four equally-sized partial-circle structures 204. Therotational paths are shown using dashed lines. As can be seen in FIG. 6,the paths of the partial-circle structures 204 reach to the center ofthe workpiece 202 and will contact substantially all interconnectstructures 16. FIG. 7 illustrates an example where the partial-circlestructures 204, 700 are larger relative to the workpiece 202. As shownin FIG. 7, all four paths substantially overlap the center of theworkpiece, thereby insuring that all interconnect structures 16 areseparated. FIG. 6 provides a benefit that the partial-circle structures204 will not interfere with one another and can be actuated (rotated)simultaneously. To the contrary, while the larger partial-circlestructures 204, 700 sweep through a larger area of the workpiece 202 andinsure that all interconnect structures 16 are removed, suchpartial-circle structures 204, 700 must be actuated (rotated)sequentially to avoid contacting each other.

FIG. 7 also illustrates that the partial-circle structures 700 do nothave to be quarter-wheels (quarter-disks). To the contrary,partial-circle structures 700 are half-disks. As would be understood byone ordinarily skilled in the art, any portion of a circle (disc) can beused depending upon the specific design requirements. Therefore,potentially any size from ¾ disk down to a very small disk portion (e.g.1/100 disk) can be utilized. In addition, the partial-circle structures204 can be replaced with any shaped device, such as a knife, stiff wire,squeegee, plow, etc. that has the capability of removing the solder frombetween the substrate 14 and the carrier 18.

In addition, the partial-circle structures 204 do not all have to be thesame size. Therefore, for example, smaller partial-circle structurescould be passed between the substrate 14 and carrier 18 followed bylarger partial-circle structures (or vice versa) in an effort to morecompletely remove all solder material from between the substrate 14 andcarrier 18. In addition, the invention is not limited to using four ofsuch a partial-circle structures. Instead, any number (e.g., 1-6, ormore) of such structures can be utilized depending upon the shape, size,etc. of the workpiece 202. For example, one large wheel could besubstituted for the plurality of wheels described. Further, theinvention can be used in serial mode with multiple fixtures, limitedonly by the capacity of the belt furnace. Also, while ball grid arraysare used in the previous example, one ordinarily skilled in the artwould readily understand that the interconnect being removed, could beany type of interconnect, such as column grid arrays, etc. In addition,the melting points and temperature hierarchies are listed for Pb soldersystems, but could be expanded to Pb free systems.

The invention described above provides an apparatus for separatingdevices joined with interconnects. The invention provides partial-circlestructures that rotate and pass between the devices to be separated. Thepartial-circle structures can be released sequentially and theinterconnect material is collected in reservoirs to preventcontamination of surrounding devices and/or the tool. The inventionsimplifies and reduces the cost of separating devices by providing anapparatus in which the workpiece can be easily mounted and thereafterplaced in any conventional heating tool. The invention operatesautomatically and on its own to break the interconnects at the propertemperature. Further, the invention holds separated devices afterremoving the interconnections to allow the devices to be easilyinspected and reworked.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1. An apparatus comprising: a frame; at least one rotationally biasedpartial-circle structure above said frame; and at least onetemperature-sensitive release operably connected to said at least onerotationally biased partial-circle structure so as to prevent rotationof said at least one rotationally biased partial-circle structure, saidframe holding a workpiece having two parts mechanically and electricallyconnected by interconnects and, at a predetermined temperature, said atleast one temperature-sensitive release releasing said at least onerotationally biased partial-circle structure such that said at least onepartial-circle structure rotates and passes between said two parts ofsaid workpiece, sweeping at least some of said interconnects out frombetween said two parts of said workpiece.
 2. The apparatus in claim 1,further comprising a plurality of rotationally biased partial-circlestructures operably connected to a plurality of correspondingtemperature-sensitive releases and said temperature-sensitive releasesbeing sensitive to different predetermined temperatures such that eachof one of said rotationally biased partial-circle structures is releasedat a different predetermined temperature.
 3. The apparatus in claim 1,further comprising a plurality of rotationally biased partial-circlestructures operably connected to a corresponding plurality oftemperature-sensitive releases and said corresponding plurality oftemperature-sensitive releases releasing said rotationally biasedpartial-circle structures so that said plurality of rotationally biasedpartial-circle structures rotate and pass between said two parts of saidworkpiece along rotational paths that partially overlap.
 4. Theapparatus in claim 1, further comprising a plurality of rotationallybiased partial-circle structures operably connected to a correspondingplurality of temperature-sensitive releases and said rotationally biasedpartial-circle structures comprising quarter-circle structures.
 5. Anapparatus comprising: a frame; a plurality of rotationally-biasedpartial-circle structures above said frame; and a correspondingplurality of temperature-sensitive releases operably connected to saidplurality of rotationally biased partial-circle structures so as toprevent rotation of said rotationally biased partial-circle structures,said frame holding a workpiece having two parts mechanically andelectrically connected by interconnects and, at a predeterminedtemperature, at least one of said temperature-sensitive releasesreleasing at least one of said rotationally biased partial-circlestructures such that said at least one of said rotationally biasedpartial-circle structures rotates and passes between said two parts ofsaid workpiece, sweeping at least some of said interconnects out frombetween said two parts of said workpiece.
 6. The apparatus in claim 5,said temperature-sensitive releases being sensitive to differentpredetermined temperatures such that each of one of said rotationallybiased partial-circle structures is released at a differentpredetermined temperature.
 7. The apparatus in claim 5, saidrotationally biased partial-circle structures comprising quarter-circlestructures.
 8. The apparatus in claim 5, said rotationally biasedpartial-circle structures each comprising less than a three-quarterportion of a disc and being approximately 0.01 inches thick.
 9. Theapparatus in claim 5, said predetermined temperature being above amelting point of said interconnects.
 10. The apparatus of claim 5, saidframe further comprising at least one reservoir positioned to receivematerial from said interconnects swept by said at least one of saidrotationally biased partial-circle structures from between said twoparts of said workpiece.
 11. The apparatus in claim 5, said plurality ofrotationally-biased partial-circle structures having overlappingrotational paths.
 12. An apparatus comprising: a frame; a plurality ofrotationally-biased partial-circle structures above said frame andhaving overlapping rotational paths; and a corresponding plurality oftemperature-sensitive releases operably connected to said plurality ofrotationally biased partial-circle structures so as to prevent rotationof said rotationally biased partial-circle structures, said frameholding a workpiece having two parts mechanically and electricallyconnected by interconnects as said apparatus is subjected to a series ofincreasingly higher predetermined temperatures and, at each one of saidpredetermined temperatures in said series, a different one of saidtemperature-sensitive releases releasing a different one of saidrotationally biased partial-circle structures such that said differentone of said rotationally biased partial-circle structures rotates andpasses between said two parts of said workpiece, sweeping at least someof said interconnects out from between said two parts of said workpiece.13. The apparatus in claim 12, said temperature-sensitive releases beingsensitive to different predetermined temperatures above a melting pointof said interconnects.
 14. The apparatus in claim 12, said rotationallybiased partial-circle structures comprising quarter-circle structures.15. The apparatus in claim 12, said rotationally biased partial-circlestructures each comprising less than a three-quarter portion of a discand being approximately 0.01 inches thick.
 16. The apparatus of claim12, said frame further comprising at least one reservoir positioned toreceive material from said interconnects swept from between said twoparts of said workpiece by said rotationally biased partial-circlestructures.